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排序方式: 共有123条查询结果,搜索用时 20 毫秒
31.
基于Mindlin解,采用三参数固体黏弹性模型,给出了盾构隧道黏弹性沉降的计算方法,通过退化验证,证明了所得出的黏弹性沉降计算方法的正确性。结合工程实例进行计算分析,分别得出了黏性系数、距开挖面距离以及开挖深度对刀盘正面摩擦、刀盘侧面摩擦、正面附加推力、盾壳与周围土体之间的摩擦力引起的地表变形的影响。计算表明:沉降稳定所需时间随黏性系数增大而延长,随开挖深度的不同而不同;不同的黏性系数,最终沉降值无明显差异;盾壳摩擦导致的沉降随距开挖面距离的增加而减小。 相似文献
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In this article, a structure that employs a Faraday shield between the Shoji antenna and the dielectric tube, which aims to reduce the dielectric wall sputtering, is investigated for the helicon wave plasma (HWP) sources. Faraday shield is usually used between the antenna and the reaction chamber to reduce the radiation from the high electromagnetic field generation, as well as to prevent the sputtering of the antenna material from polluting the reaction chamber during the discharge. Here, the influence of the Faraday shield on the longitudinal and radial electric field of the antenna is analysed through COMSOL MultiphysicsTM. Significant attenuations of both the longitudinal and radial fields are observed in the presence of the shield. In addition, by comparing the electric field distribution under two different shielding parameters, it is found that the shielding effects are not the same. Therefore, a detailed study of two kinds of design (pitch and gap) for the shield was carried out. The results show that the pitch has a little impact on the overall shielding effect when the gap is unaltered. The best shielding performance appears when we set the pitch at T of 8 and 10. In addition, the shielding effect also becomes worse as the gap increases while the pitch remains unchanged. A relatively good shielding effect can be produced by setting the gap to the value of 4–8 mm (a gap/pitch ratio of 2/15–4/15). This work provides a theoretical basis for designing a Faraday shield structure between the antenna and the dielectric tube, which is helpful to realize stable and controllable HWP discharges. 相似文献
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屏蔽厂房是AP1000核岛厂房的第一层外部防线,确保屏蔽厂房在服役期间遭受爆炸冲击荷载作用下的安全性和完整性,十分重要。本文中,采用欧拉-拉格朗日算法(coupled Euler-Lagrange, CEL),对炸药在屏蔽厂房20种不同起爆部位作用下的动态破坏特征进行了研究,以结构贯穿破坏的损伤质量作为损伤程度的判别依据,着重探讨在不同起爆位置作用下结构的压力和损伤演化特性。研究表明:在接触爆炸荷载作用下,厂房在起爆点附近发生局部破坏;在相同高度下,环向不同角度起爆所引起的损伤程度差异较小,不同高度起爆的损伤程度差异较大。通过压力和损伤的演化分析,确定了屏蔽厂房最不利抗爆部位,对厂房不同部位的配筋策略提出建议。结论可为制定屏蔽厂房在爆炸冲击荷载作用下的安全防护措施提供参考依据。
相似文献36.
层状陶瓷材料的电磁屏蔽效能对结构功能一体化层状陶瓷材料的设计具有重要影响。采用流延法与化学气相渗透(chemical vapor infiltration,CVI)工艺相结合制备SiC_w/Si C层状陶瓷,研究碳化硅颗粒(Si C particle,SiCp)、氮化硅颗粒(Si_3N_4particle,Si_3N_4p)对SiC_w/Si C层状陶瓷电磁屏蔽性能的影响。结果表明:SiC_w/Si C层状陶瓷具有较高的电磁屏蔽性能,颗粒的加入有助于提高层状陶瓷的电磁屏蔽性能。颗粒粒径越小,材料的电磁屏蔽性能越好;并且SiCp的电磁屏蔽作用强于Si_3N_4p。 相似文献
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Computed tomography (CT) uses a high dose of radiation to create images of the body. As patients are exposed to radiation during a CT scan, the use of shielding materials becomes essential in CT scanning. This study was focused on the radiation shielding materials used for patients during a CT scan. In this study, sheets were manufactured to shield the eyes and the thyroid, the most sensitive parts of the body, against radiation exposure during a CT scan. These sheets are manufactured using silicone polymers, barium sulfate (BaSO4) and tungsten, with the aim of making these sheets equally or more effective in radiation shielding and more cost-effective than lead sheets. The use of barium sulfate drew more attention than tungsten due to its higher cost-effectiveness. The barium sulfate sheets were coated to form a multigate structure by applying the maximum charge rate during the agitator and subsequent mixing processes and creating multilayered structures on the surface. To measure radiation shielding effectiveness, the radiation dose was measured around both eyes and the thyroid gland using sheets in three different thicknesses (1, 2 and 3 mm). Among the 1 and 2 mm sheets, the Pb sheets exhibited greater effectiveness in radiation shielding around both eyes, but the W sheets were more effective in radiation shielding around the thyroid gland. In the 3 mm sheets, the Pb sheet also attenuated a higher amount of radiation around both eyes while the W sheet was more effective around the thyroid gland. In conclusion, the sheets made from barium sulfate and tungsten proved highly effective in shielding against low-dose radiation in CT scans without causing ill-health effects, unlike lead. 相似文献
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在弹道段撞击速度范围内,针对玄武岩纤维布/铝板组合防护结构开展了高速撞击实验(实验使用的2017铝球弹丸的直径为3.97 mm,撞击速度为1.49~3.65 km/s),获得了防护结构的弹道极限速度,分析了铝球弹丸高速击穿玄武岩纤维布和铝板后的剩余速度。基于单层铝板发生穿孔失效时的临界撞击动能,研究了玄武岩纤维布/铝板组合防护结构的高速撞击防护性能。结果表明:当弹丸未破碎时,相同直径的铝球弹丸以不同速度击穿相同面密度的玄武岩纤维布后的速度减小量近似为常数;铝球弹丸直径越大,弹丸击穿相同面密度的玄武岩纤维布后的速度减小量越小;在防护结构面密度相同的情况下,铝板前置的玄武岩纤维布/铝板组合防护结构比玄武岩纤维布前置的组合防护结构具有更好的高速撞击防护性能。 相似文献
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